<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .father {
      width: 400px;
      height: 400px;
      background-color: skyblue;

      /* text-align: center; */
      /* margin: 0 auto; */
    }

    .son {
      width: 100px;
      height: 100px;
      background-color: orange;
      margin: 0 auto;
    }

  </style>
</head>
<body>
  <div class="father">
    <div class="son"></div>
  </div>
</body>
</html>